A promoter is a DNA sequence located in the flanking regions of a gene. Expression of a gene is initiated at a gene transcription site, which in turn mainly depends on the RNA polymerase and cis-regulatory elements in the promoter regions.
Root tissue is very important in plant development. However, the state of the art with respect to understanding the regulation of gene expression in roots is still very limited. Cis-regulatory elements of promoters that exclusively confer root-specific expression have not been described in the literature, and only a few root-specific promoters have been described at all. Recently, an Arabidopsis gene (pyk10) promoter has been reported to drive gene expression in root in mature transgenic plants, but there is also extensive expression in different parts of a seedling (Nitz et al 2001 Plant Sci. 161: 337-346). Short elements that contribute to root-preferred expression have been revealed and been shown to be involved predominantly in root-specific expression as enhancers, such as the ocs-elements, ocs-like mas-elements and as-l-elements (Ellis et al 1987, EMBOJ., 6 :3203-3208; Feltkamp et al. 1995, Plant Sci. 109 :57-65; Lam et al., 1989, PNAS (USA), 86 :7890-7894.)
Tissue-specific expression is believed to be due to the interaction of a set of regulatory proteins that bind to a special combinatory set of cis-regulatory elements of the promoter. Therefore, the expression pattern of a designed gene is determined by trans-factors, the transcription factor proteins available from the background cells and cis-factors the cis-regulatory elements in the DNA sequences of gene regions. Most of cis-regulatory elements are located in the proximal region about 500 bp from the transcription start site. But some of them are found in the intron, coding region and downstream region, or in the distal region as far as 10 kb from start codon.
Root specific promoters are of special interest because of physiological functions in root and its vulnerability to many pathogens and pests.
Genetic engineering techniques provide a method to introduce useful traits to plants, but require a variety of tissue-specific promoters to express heterogeneous genes in the appropriate plant tissues. Root-specific promoters would have potential applications to promote expression of endogenous or heterogeneous genes in roots to enhance plant resistance to pathogens and pests; stress tolerance to heat, salt or drought; and improve absorbency of soil nutrients; and production of recombinant proteins aimed at molecular farming and phytoremediation.
Transgenic plants expressing polypeptides with anti-pathogen or anti-pest activity can be used to decrease crop or forest damage and loss. However, high levels of heterogeneous gene expression in other parts of plants may cause negative effects on plant growth and reproduction, and also cause selective pressure for pathogens or pests to develop resistance. Accordingly, tissue-specific expression is desirable in most cases of plant genetic engineering. Only a few promoters from angiosperms have been identified to be expressed in root tissues. (For example, see: U.S. Pat. No. 5,023,179, WO0153,502, U.S. Pat. No. 5,459,252, and U.S. Pat. No. 5,837,876.) These are angiosperm promoters whose function in gymnosperms is unknown
Thus, it is an object of the invention to provide a promoter suitable for use in plant cells.